Battery Pack

ABSTRACT

Provided is a battery pack including: a first battery group in which a plurality of storage batteries having a battery can side surface and a battery can bottom surface linked to the battery can side surface are laminated so that the battery can side surfaces face each other; a second battery group in which a plurality of storage batteries having a battery can side surface and a battery can bottom surface linked to the battery can side surface are laminated so that the battery can side surfaces are face each other; and a case housing the first battery group and the second battery group, wherein the facing surfaces of the first battery group and the second battery group are directly or indirectly thermally connected to each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/333,957, filed Mar. 15, 2019, which is a Continuation Application ofPCT Application No. PCT/JP2018/008369, filed Mar. 5, 2018, which claimspriority to Japanese Patent Application No. 2017-064157, filed Mar. 29,2017, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a battery pack.

BACKGROUND ART

Recently, a demand for an in-vehicle secondary battery has increasedagainst the background of environmental regulations. Among the secondarybatteries, since a lithium ion secondary battery usually has a highdischarge potential as compared with a lead battery, a nickel hydrogenbattery, or the like, the lithium ion secondary battery can beminiaturized or have a higher energy density, and thus, is considered asbeing promising. For example, further higher energy density, higheroutput density, longer life, and the like are required for the lithiumion secondary battery for real application. For higher output of abattery, it is effective to input and output a large current from thebattery as well as higher potential. However, when a large current isinput and output from a battery, heat derived from internal resistanceof the battery is produced inside the battery. When the produced heat isnot sufficiently removed from the battery, battery temperature israised. Battery characteristics such as battery capacity or internalresistance of a lithium ion battery have a different deterioration trenddepending on a battery temperature, and particularly when the batterytemperature is higher, the battery characteristics are often lowered.Thus, development of a technology to improve heat dissipationperformance of a battery is needed.

When a plurality of lithium ion unit cells (hereinafter, referred to asunit cells) is combined and used as a battery group (for example, usedas a battery module or a battery pack), it is desired to decrease atemperature difference between unit cells of the battery group. This isbecause when the temperature difference between the unit cells is large,a difference in deterioration between the unit cells easily occurs.Since the characteristics of the battery group tend to berate-determined by the characteristics of the most deteriorated cellamong the unit cells included in the battery group, design of thebattery group avoiding a structure in which a specific cell isdeteriorated is needed.

Thus, a technology in which in a battery group formed by combining aplurality of unit cells, a temperature difference between unit cells isdecreased is being developed. Specifically, PTL 1 discloses a storagebattery in which an electrolytic bath housing a unit cell is formed of acuboid composed of a short side having a narrow width and a long sidehaving a wide width, and a plurality of unit cells is linked so as to beadjacent to each other between the short sides of the electrolytic bathto form an aggregate battery having a required power capacity.

Meanwhile, when a large current is input and output from a battery, across-sectional area of a cable connected to the battery is needed to beincreased. As a material used in the cable, a metal represented bycopper is used, however, the metal has a high thermal conductivity, andthus, has high heat dissipation performance.

CITATION LIST Patent Literature

PTL 1: JP 2000-164186 A

SUMMARY OF INVENTION Technical Problem

In the technology described in PTL 1, a plurality of ribs is formed on along side of an electrolytic bath of each unit cell. Then, air and thelike are forcibly flowed between the ribs to cool the unit cell. In thisconfiguration, when cooling efficiency is decreased (for example, a flowrate of forcibly flowed air is small, or an input/output current islarge and a heating value of the unit cell is large), a batterytemperature distribution occurs in a battery group to be configured, andparticularly, a battery temperature of the unit cell disposed near acenter of the long side of the battery group is high, so that there is arisk of deterioration progression. The present invention has been madein view of the above problem, and an object of the present invention isto provide a battery pack having a small temperature difference betweenbattery groups.

Solution to Problem

A battery pack of an embodiment of the present invention includes afirst battery group in which a plurality of storage batteries having abattery can side surface and a battery can bottom surface linked to thebattery can side surface are laminated so that the battery can sidesurfaces face each other; a second battery group in which a plurality ofstorage batteries having a battery can side surface and a battery canbottom surface linked to the battery can side surface are laminated sothat the battery can side surfaces face each other; and a case housingthe first battery group and the second battery group, wherein the facingsurfaces of the first battery group and the second battery group aredirectly or indirectly thermally connected to each other.

Advantageous Effects of Invention

According to the invention, a battery pack having a small temperaturedifference between battery groups can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing for describing an example of a specificconfiguration of a battery group in Example 1.

FIG. 2 is a drawing for describing an example of a specificconfiguration of a battery group in Example 2.

FIG. 3 is a drawing for describing an example of a specificconfiguration of a battery group in Example 5.

FIG. 4 is a drawing for describing an example of a specificconfiguration of a battery group in Example 6.

FIG. 5 is a drawing for describing an example of a specificconfiguration of a battery group in Example 7.

FIG. 6 is a drawing for describing an example of a specificconfiguration of a battery group in Comparative Example 1.

FIG. 7 is a drawing for describing an example of a specificconfiguration of a battery group in Comparative Example 2.

FIG. 8 is a temperature rise ratio chart representing a temperature riseof each unit cell of the configurations of Examples 1 and 2 and theconventional configuration from an environmental temperature, as a ratiofrom a lowest temperature in a battery group.

FIG. 9 is a temperature rise ratio chart representing a temperature riseof each unit cell of the configurations of Examples 3 and 4 and theconventional configuration from an environmental temperature, as a ratiofrom a lowest temperature in a battery group.

FIG. 10 is a temperature rise ratio chart representing a temperaturerise of each unit cell of the configurations of Examples 5 and 6 and theconventional configuration from an environmental temperature, as a ratiofrom a lowest temperature in a battery group.

FIG. 11 is a temperature rise ratio chart representing a temperaturerise of each unit cell of the configuration of Example 7 and theconventional configuration from an environmental temperature, as a ratiofrom a lowest temperature in a battery group.

FIG. 12 is a drawing in which the battery pack of FIG. 2 is viewed froman upper surface.

FIG. 13 is a first modified example of FIG. 12.

FIG. 14 is a second modified example of FIG. 12.

FIG. 15 is a perspective view of the secondary battery of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described. However, theembodiments do not limit the following descriptions, and can beoptionally modified and carried out within the range not departing fromthe gist of the present invention.

The present embodiments will be described in detail. As a secondarybattery in the present embodiment, a lithium ion secondary battery isused; however, the present configuration can be also applied to othertypes of storage battery. In addition, the effect can be obtained withany constituent member of the lithium ion secondary battery. That is, inthe present invention, an electrode composed of an Al current collectorfoil and a positive electrode material having a layered structure as apositive electrode, and an electrode composed of a Cu current collectorfoil and a carbon material as a negative electrode are used, but otherconfigurations may be also used. For example, as described in Examples 3and 4, heat dissipation properties may be improved even in the case ofusing an Al foil in the negative electrode. A cooling environment is anexample, and it can be applied also to the case of using otherrefrigerants. In addition, as a shape of the lithium ion battery, arectangular battery was used in the present Example; however, the effectcan be obtained even with the battery known as having other shapes, forexample, a laminate type, a cylindrical shape, or the like.

When unit cells are used as a battery group, the unit cells areconnected to each other in series or in parallel. In this case, forguaranteeing safety, a member capable of securing insulation betweenbatteries may be introduced around the unit cell, for example, as shownin Example 7. The shape of the member is free and the material can befreely selected; however, it is preferred to include a heat transfermember. When the unit cells are connected to each other in series or inparallel, wiring to be used is not particularly limited; however, forexample, a bus bar can be used. Whatever the form of serial or parallelconnection is, the effect is exhibited when the battery arrangement andthe configuration of an external terminal according to the presentinvention are used. For example, even with a battery group in which sixbattery groups having two parallel parts are arranged in series, theeffect of the present invention is obtained. In addition, it ispreferred that in the battery group, in addition to electricallyconnecting the unit cells to each other in series or in parallel, theunit cells are physically bound to each other using a fixing jig.However, the present invention is not limited to the binding method. Forexample, the effect was exhibited even when two battery groups aresecured using a set of fixing jigs or secured using two sets of securingjigs.

In the present invention, the battery pack is configured using a firstbattery group and a second battery group which are connected by theabove-described means as a basic configuration, and in addition to them,the battery pack may be provided with a control device of a battery (forexample, a Battery Management System; BMS or the like can be used) or asafety mechanism (for example, a fuse or the like), and even in the caseof connecting them to wiring in the battery group, the effect of thepresent invention is obtained.

A method of contacting a case bottom surface with the battery group isnot particularly limited and the effect of the present invention isexhibited even with for example, adhesion with an adhesive or the likeor connection through a fixture using bolts or nuts. The shape of thecase is exemplified by a cuboid in the present embodiment, however, theshape is not particularly limited. In addition, the effect of thepresent invention is not limited to a current application condition tothe battery pack or a cooling condition.

Hereinafter, the present invention will be described in detail, based onthe Examples and the Comparative Examples. FIG. 1 is an explodedperspective view of a battery pack 100 of the present invention. Inaddition, when up, down, left, right, front, or rear is referred to inthe following description, it follows the directions as indicated in thelower left in each drawing.

The battery pack 100 is composed of a first battery group 10A, a secondbattery group 10B, and a case 5 (5 a, 5 b) housing the first batterygroup 10A and the second battery group 10B. The case 5 is composed of acase 5 a and a cover 5 b covering a case opening. In addition, in thepresent embodiment, a bottom surface 5 b is provided as an additionalmember; however, a structure in which the case 5 a is provided with abottom surface and has an opening on an upper surface, and a cover 5 bis disposed on the upper surface may be also used.

FIG. 15 is a drawing representing a storage battery 1 used in thepresent invention. The storage battery 1 is composed of a pair of widesurfaces 1 a, a pair of narrow surfaces 1 b, a bottom surface 1 c, and acover 1 d. The cover 1 d is provided with a positive electrode externalterminal 2 a and a negative electrode external terminal 2 b.

Referring back to FIG. 1, the first battery group 10A and the secondbattery group 10B are described, respectively. The first battery group10A is formed by laminating a plurality of the storage batteries 1 (inthe present embodiment, six storage batteries) so that the wide surfaces1 a of the storage battery 1 face each other. For the second batterygroup 10B also, like the first battery group 10A, a structure is formedby laminating the storage batteries so that the wide surfaces of thestorage battery face each other.

The storage batteries 1 constituting the first battery group 10A areconnected to each other in series by a bus bar 2. In addition, like thesecond battery group 10B, the storage batteries 1 are connected to eachother in series by the bus bar 2. In addition, a structure in which thestorage battery 1 on a bottom surface 5 b side of the first batterygroup 10A and the storage battery 1 on a bottom surface 5 b side of thesecond battery group 10B no are connected to each other by the bus bar 2is formed. Further, each of the two battery groups 10A and 10B has anexternal terminal 3 which is connected to other electronic components(for example, a junction box or the like) housed in the battery pack100, disposed on the upper center side of the battery pack 100. In thepresent invention, a temperature change of the battery pack 100 wasmeasured by some settings (FIGS. 1 to 7).

EXAMPLE 1

First, Example 1 is described. A first battery group and a secondbattery group were horizontally arranged as shown in FIG. 1 and thenthermally directly connected, and a HV cable made of copper having adiameter of 95 mm was installed at the end of a positive electrodeexternal terminal and a negative electrode external terminal and acurrent was applied thereto. A heating value from the battery at thattime was 3 W on average.

In addition, as a cooling condition, air at a wind speed of 5 m/sec wasapplied only to a bottom plate with a case in a lower portion of thebattery group interposed therebetween. In FIG. 1, an upper surface ofthe case is shown. FIG. 8 shows the results when the state is almostnormal, after applying the condition to the battery pack.

EXAMPLE 2

Subsequently, Example 2 is described. Example 2 is different fromExample 1 in that after the first battery group and the second batterygroup were horizontally arranged, a heat transfer member 6 (heatconductive member) in a planar shape was interposed therebetween.

In FIG. 2, a structure of the present Example is shown. In the presentExample, as described above, the heat transfer member 6 was disposedbetween the first battery group 10A and the second battery group 10B.The heat transfer member had two types, one having a thickness of 3 mmand the other having a thickness of 15 mm, and a temperature rise of thebattery pack 100 was measured when each of the heat transfer members wasused. The results are shown in FIG. 8. In addition, the coolingcondition and the current application condition were identical to thoseof Example 1.

EXAMPLE 3

Subsequently, Example 3 is described. Example 3 is different fromExample 1 in that as the material of the negative electrode currentcollector foil, an aluminum current collector foil was used instead of acopper foil.

Since the detailed structure of the battery pack 100 is in the samearrangement as that of FIG. 1, the description thereof is omitted. Theresults of a temperature rise of the battery pack 100 are shown in FIG.9. In addition, the cooling condition and the current applicationcondition were identical to those of Example 1.

EXAMPLE 4

Subsequently, Example 4 is described. Example 4 is different fromExample 2 in that as the material of the negative electrode currentcollector foil, an aluminum current collector foil was used instead of acopper foil. Since the detailed structure of the battery pack 100 is inthe same arrangement as the arrangement of FIG. 2, the descriptionthereof is omitted. In the present embodiment, as the heat transfermember 6, a member having a thickness of 15 mm is used. The results of atemperature rise of the battery pack 100 are described in FIG. 9. Inaddition, the cooling condition and the current application conditionwere identical to those of Example 1.

EXAMPLE 5

Subsequently, Example 5 is described. Example 5 is different fromExample 1 in that the first battery group 10A and the second batterygroup 10B were vertically arranged as in FIG. 3 and a narrow sidesurface of the storage battery constituting the battery group was incontact with the bottom surface of the case 5 of the battery pack 100.The results of a temperature rise of the battery pack 100 are describedin FIG. 10. In addition, the cooling condition and the currentapplication condition were identical to those of Example 1.

EXAMPLE 6

Subsequently, Example 6 is described. Example 6 is different fromExample 2 in that the first battery group and the second battery groupwere vertically arranged as in FIG. 4, and a narrow side surface of thestorage battery constituting the battery group was in contact with thebottom surface of the case 5 of the battery pack 100.

In addition, in the present Example, similarly to Example 2, the heattransfer member 6 had two types, one having a thickness of 3 mm and theother having a thickness of 15 mm, and each measurement results areshown in FIG. 10. In addition, the cooling condition and the currentapplication condition were identical to those of Example 1.

EXAMPLE 7

Subsequently, Example 7 is described. Unlike Examples 1 to 6, thepresent Example has a structure in which the first battery group and thesecond battery group, each of which had 6 storage batteries 1 connectedin series, were connected to each other in series, and the bottomsurface of the storage battery 1 was in contact with the bottom surface5 b of the case of the battery pack 100. In addition, in the presentembodiment also, the heat transfer member 6 was disposed between thefirst battery group 10A and the second battery group 10B. As the heattransfer member 6, an aluminum flat plate having a plate thickness of 15mm was used. The results of a temperature rise of the battery pack 100are shown in FIG. 11. In addition, the cooling condition and the currentapplication condition were identical to those of Example 1.

COMPARATIVE EXAMPLE 1

Subsequently, Comparative Example 1 is described. Comparative Example 1is different from Examples 1 to 7 in that the battery group is notdivided into two and is laminated as a single battery group.

FIG. 6 is a drawing of the battery pack 100 of Comparative Example 1.Twelve batteries 1 were linked in series to form a single battery group,which was disposed so that the wide surface 1 a of the unit cell 1 wasin contact with the bottom surface 5 b of the case 5. The results of atemperature rise of the battery pack 100 are shown in FIGS. 8 and 9. Inaddition, the cooling condition and the current application conditionwere identical to those of Example 1.

COMPARATIVE EXAMPLE 2

Subsequently, Comparative Example 2 is described. Comparative Example 2is different from Examples 1 to 7 in that the battery group was notdivided into two and laminated as a single battery group, and the narrowsurface 1 b of the unit cell 1 was in contact with the bottom surface 5b of the case 5.

FIG. 7 is a drawing of the battery pack 100 of Comparative Example 2.Twelve batteries were linked in series to form a single battery group,which was disposed so that the narrow surface 1 b of the unit cell 1 wasin contact with the bottom surface 5 b of the case 5. The results of atemperature rise of the battery pack 100 are shown in FIGS. 10 and 11.In addition, the cooling condition and the current application conditionwere identical to those of Example 1. Hereinafter, the effects of thepresent patent application will be described based on the results of theExamples and the Comparative Examples.

As a result of imparting the conditions represented in the presentExamples and the Comparative Examples to the battery group, when thetemperature of the battery group reaches an almost steady state, thebattery temperature was raised as compared with the environmentaltemperature. FIGS. 8 to 11 are drawings which show a ratio of a risingtemperature of each unit cell of the battery group compared with anenvironmental temperature to a rising temperature of the unit cellhaving the smallest temperature rise, for each cell. In the drawings,the cell No. corresponds to the cell No. described in the drawingcorresponding to each Example or Comparative Example. Here, for twobattery groups in the Examples, the unit cells present in the placewhere the battery groups face each other had almost the sametemperature, and the description thereof is omitted for simplicity.Hereinafter, the result of each drawing will be described in detail.

FIG. 8 shows a temperature rise ratio of the configurations of Examples1 and 2, which are examples of applying the present invention to thebattery arrangement which is horizontally arranged as in ComparativeExample 1. It can be seen from the drawing that in the ComparativeExample as the conventional configuration, the temperature of cell No.7, which is disposed at a center of the laminate of a battery, washighest. This is because in the battery near cell No. 7, heat quantityproduced from the surrounding battery was not dissipated to raise thetemperature of the surrounding battery as well as the temperature of thebattery itself, and thus, there was no temperature difference to makeheat difficult to flow, resulting in a battery temperature rise.Meanwhile, the unit cell of cell No. 1 in contact with the case bottomsurface and the battery of cell No. 12 having the external terminal hada heat dissipation path to suppress a temperature rise. From theresults, since there occurred a difference in the temperature risebetween cell No. 1 and No. 12 and cell No. 7, the temperature rise ratiowas greatly changed in the same battery group in Comparative Example 1.Therefore, it can be seen that the temperature difference between theunit cells easily occurred in Comparative Example 1.

Meanwhile, FIG. 8 shows the example of the present invention. It can beseen that the present invention can reduce the temperature rise rate inthe entire cells as compared with the Comparative Example, from thecomparison of the temperature rise rates of the batteries in the entirecells present in the same arrangement. In addition, as shown in Example2, it can be seen that the effect was further exhibited by disposing theheat transfer member between the battery groups, thereby reducing thetemperature difference between the batteries. This means that the heatdissipation path was effectively secured by disposing the externalterminal in cell No. 6 which had the highest temperature. Additionally,it can be seen that in Example 2, an Al plate was introduced to securethe heat dissipation path, and thus, the rising temperature differencebetween batteries could be effectively reduced.

FIG. 9 shows the temperature rise rates of the configurations ofExamples 3 and 4 which are examples of applying the present invention tothe battery configuration which was horizontally arranged as inComparative Example 1. It can be seen from the drawings that when thenegative electrode current collector foil was Al also, the temperaturedifference between batteries tended to be reduced as illustrated in FIG.8. Heat behavior which occurred in FIG. 9 is due to the same phenomenonas that occurred in FIG. 8.

FIG. 10 shows the configurations of Examples 5 and 6 which are examplesof applying the present invention to the battery configuration which wasvertically arranged as in Comparative Example 2. It can be seen from thedrawing that in the Comparative Example as the conventionalconfiguration, the temperature of cell No. 6 which is at the center ofthe laminate of the battery was highest. The temperature rise occurredhere is due to the same phenomenon as that in the Comparative Example 1shown in FIG. 8.

In addition, it can be seen from the drawing that in the case ofvertical arrangement also, the temperature difference between batterieswas reduced like FIGS. 8 and 9. Even in the case of the verticalarrangement not the horizontal arrangement, the temperature near thecenter of the long side tended to be raised. It can be seen that bydisposing the external terminal in the portion, the same effect as thatin FIGS. 8 and 9 was obtained and the rising temperature differencecould be reduced.

In FIG. 11, the temperature difference of the case of applying thepresent invention to the configuration shown in Example 7 is comparedwith the battery configuration of the vertical arrangement likeComparative Example 2. It can be seen from the drawing that the presentinvention also tended to reduce the temperature difference. It can beseen that it is because in Example 7 also, the external terminal wasinstalled in cell No. 6 which has the highest battery temperature,thereby effectively dissipating heat to the outside of the batterygroup.

The battery pack described in the present invention includes a firstbattery group (10A) in which a plurality of storage batteries (1) havinga battery can side surface (1 a, 1 b) and a battery can bottom surface(1 c) linked to the battery can side surface (1 a, 1 b) are laminated sothat the battery can side surfaces (1 a, 1 b) face each other; a secondbattery group (10B) in which a plurality of storage batteries (1) havinga battery can side surface (1 a, 1 b) and a battery can bottom surface(1 c) linked to the battery can side surface (1 a, 1 b) are laminated sothat the battery can side surfaces (1 a, 1 b) face each other; and acase (5) housing the first battery group (10A) and the second batterygroup (10B), wherein facing surfaces of the first battery group (10A)and the second battery group (10B) are directly or indirectly thermallyconnected to each other. By having this structure, a battery pack havinga decreased temperature difference between the battery groups can beprovided.

In addition, the present invention has a structure in which widesurfaces (1 a) of the two battery groups face the bottom surface of thecase (5). By having this structure, a cooling area is increased toimprove cooling performance as compared with the case in which thenarrow surface 1 b is in contact with the case 5.

In addition, in the battery pack described in the present invention,when the wide surface 1 a of the battery 1 faces downward, the externalterminal 3 is at the center side of the battery pack, thereby coolingthe center side of the battery pack which is more difficult to dissipateheat through the external terminal. Thus, the heat dissipationproperties are further improved, thereby making it possible to provide abattery pack having a decreased temperature difference between thebattery groups.

In addition, as shown in FIG. 12, in the battery pack described in thepresent invention, the first heat transfer member (6) is disposedbetween the first battery group (10A) and the second battery group(10B), and the heat transfer member (6) is closely adhered to the firstbattery group (10A) and the second battery group (10B). By having thisstructure, thermal diffusion is further promoted by the heat transfermember, thereby providing a battery pack having a decreased temperaturedifference between the battery groups. In addition, FIG. 12 is a drawingin which FIG. 2 is viewed from the upper surface.

In addition, in the battery pack described in the present invention, asshown in FIG. 13, the second heat transfer member 61 and the third heattransfer member 62 may be disposed on both sides of the first batterygroup 10A and the second battery group 10B. In this case, the firstbattery group 10A is sandwiched between the heat transfer member 6 andthe second heat transfer member 61, and the second battery group 10B issandwiched between the heat transfer member 6 and the third heattransfer member 10B, so that the heat dissipation properties areimproved also on both sides of the battery groups 10A and 10B, therebyproviding a battery pack having a further decreased temperaturedifference between the battery groups.

In addition, the battery pack described in the present invention has astructure in which for both of the second heat transfer member 61 andthe third heat transfer member 62, those having a larger width, that is,a larger thickness than the first heat transfer member 6 are used. Byhaving this structure, the structure becomes large so that the case 5and the heat transfer members 61 and 62 can be fixed with a screw andthe like, so that the case 5 and the heat transfer members 61 and 62 canbe more closely adhered. Thus, it becomes easy to transfer heat of thebattery 1 to the case 5, thereby providing a battery pack havingimproved cooling performance.

In addition, in the battery pack described in the present invention, asanother form different from that as shown in FIG. 14, the first heattransfer member 6 has a larger thickness than the second heat transfermember 61 and the third heat transfer member 62. By having thisstructure, thermal diffusion between the two battery groups having theworst heat dissipation properties is further promoted, thereby providinga battery pack having improved cooling performance. In addition, in thepresent invention, the battery pack type of contacting the wide surface1 a of the battery 1 as described above with the bottom surface of thecase 5 exerts the effect very much when it is used for natural coolinglike the case in which cooling air is not flowed between the batterygroups or the unit cells. Therefore, the present invention is veryappropriate for a structure in which the battery 1 is horizontallyarranged.

As described above, the embodiments of the present invention have beendescribed in detail; however, the present invention is not limited tothe above embodiments, and various design modifications can be madewithin the range not departing from the spirit of the present inventiondescribed in the claims. For example, the foregoing embodiments havebeen described in detail for better understanding of the presentinvention, and are not necessarily limited to those having all of theconfiguration described above. In addition, some of the configurationsof any embodiment can be replaced with the configurations of anotherembodiment, and to the configurations of any embodiment, theconfigurations of another embodiment can be added. In addition, some ofthe configurations of each embodiment can be deleted or substituted, orother configuration can be added thereto.

The following content of disclosure of priority basic application isincorporated herein as a cited reference.

Japanese Patent Application No. 2017-064157 (filed on Mar. 29, 2017).

REFERENCE SIGNS LIST

-   1 unit cell-   2 wiring-   3 external terminal 5 case-   6, 61, 62 heat transfer member

1. A battery pack comprising: a first battery group and a second batterygroup in each of which a plurality of storage batteries are laminated,with each storage battery formed in a cuboid composed of wide surfacesand narrow surfaces, so that the wide surfaces are placed to face eachother; a bus bar for connecting the first battery group and the secondbattery group together; and a first external terminal for connecting thefirst battery group to an electronic circuit and a second externalterminal for connecting the second battery group to the electroniccircuit, wherein the first battery group and the second battery groupare disposed side by side inside a case housing so that the narrowsurfaces of the first battery group and the narrow surfaces of thesecond battery group face each other; and wherein the first externalterminal is disposed on the narrow surfaces of the first battery groupand the second external terminal is disposed on the narrow surfaces ofthe second battery group so that the first external terminal and thesecond external terminal face each other.
 2. The battery pack accordingto claim 1, wherein a storage battery on a top surface of each of thefirst battery group and the second battery group is provided with thefirst external terminal and the second external terminal.
 3. The batterypack according to claim 1, wherein the first external terminal and thesecond external terminal are provided around a center of the batterypack.
 4. The battery pack according to claim 1, wherein additionalnarrow surfaces of each of the first battery group and the secondbattery group, which are not the narrow surfaces of the first batterygroup and the second battery group placed to face each other, areprovided with the first external terminal and the second externalterminal.
 5. The battery pack according to claim 2, wherein the firstexternal terminal and the second external terminal are provided around acenter of the battery pack.
 6. The battery pack according to claim 2,wherein additional narrow surfaces of each of the first battery groupand the second battery group, which are not the narrow surfaces of thefirst battery group and the second battery group placed to face eachother, are provided with the first external terminal and the secondexternal terminal.
 7. The battery pack according to claim 3, whereinadditional narrow surfaces of each of the first battery group and thesecond battery group, which are not the narrow surfaces of the firstbattery group and the second battery group placed to face each other,are provided with the first external terminal and the second externalterminal.